Tone control system



P. F. G. HOLST TONE CONTROL SYSTEM Sept. 7, 1937.

Filed May 3l, 1935 2 Sheets-Sheet 1 .'91 NON Sept. 7, 1937. P. F. G.HoLsT 2,092,070

" vTONE CONTROL SYSTEM Filed May 31, 1955 2 sheets-sheet 2 R55 PONCE CH14 R19 C TER/5 77C.

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tutti@ A T E TONE CONTROL SYSTEM Poul F. G. Holst, Audubon,

N. J., assignor to Radio Corporation of America, a corporation or"Delaware Application May 31, 1935, Serial No. 24,245

17 Claims.

The present invention relates to tone control systems for radioreceiving systems and has, for its primary object, to provide animproved tone control system which may provide audio frequencycompensation in predetermined relation to changes in selectivity of thehigh frequency circuits, to provide a predetermined frequency responsein the system.

It is a further objectl of the present invention to provide tonecompensating means in a plurality of audio frequency amplifier circuitsand in one or more high frequency amplifier circuits of a radioreceiving system, the high frequency amplifier control means beingarranged to Vary the selectivity of the receiving system, and the audiofrequency control means being arranged to vary or adjust the audiofrequency response characteristic, in cooperative relation to the firstnamed control means, whereby the over-all fidelity of the receivingsystem may be controlled in a predetermined manner.

It is also an object of the present invention to provide uni-controladjustment of the audio frequency output characteristic of a radioreceiving system by simultaneous adjustment of tone cornpensatingnetworks in one or more audio frequency stages and selectivity controlelements associated with the high frequency signal circuit.

'I'he invention further relates specifically to multi-range radioreceiving systems having wave band selector means whereby the receiveris responsive to radio signals in a plurality of differing wave bands,and has, for its further object, to provide means connected with thewave band selector means for the uni-control adjustment of the audiofrequency response characteristic of the system, and the selectivitycharacteristic in predetermined mutual relation, whereby a predeterminedover-all response characteristic is obtained for each differing waveband.

Further, in accordance with the invention, in addition to the tonecontrol system comprising simultaneously adjustable uni-control highfrequency and low frequency circuits, whereby the selectivity and audiofrequency response are adjustable by common means in predeterminedmutual relationship, separate and independent filters, manual tone andvolume control means are interposed in the radio receiving systempreferably between the high receiving circuits and the audio frequencyamplifier circuits and, accordingly, it is a further object of thepresent invention to provide independent manual tone and volume controlmeans and the like in a radio signal receiving system between the highfrequency (Cl. Z50-20) and low frequency circuits comprising theadjustable tone control system, as hereinbefore referred to.

The invention will, however, be better understood from the followingdescription when considered in connection with the accompanyingdrawings, and its scope will be pointed out in the appended claims.

In the drawings, Figure l is a schematic circuit diagram of asuperheterodyne radio receiving 10 system embodying the invention, and

Figs. 2 and 3 are graphs or curves illustrating certain audio frequencyresponse characteristics of the system in Fig. 1.

Referring to Fig. l, a radio receiving system of 15 the superheterodynetype is provided with adjustable selectivity control means in aplurality of high frequency receiving circuits such, for example, as theintermediate frequency amplifier circuits. The latter circuits areillustrated in the 20` gure in connection with the usual higherfrequency receiving means indicated in the block enclosure 5. Thereceiving means is indicated as being provided with a wave band selectormeans for ve different wave bands designated by the 25 letters X, A, B,C and D, having a movable control element l.

The receiver is supplied with radio signals from any suitable source,such as antenna and ground means 9, and produces an intermediatefrequency 30 signal in the output leads indicated at il. The outputleads are coupled to the first intermediate frequency amplifier tube I3through tuned transformer coupling means adapted to provide adjustmentselectively and comprising a primary 35 winding l5 connected with theintermediate frequency output leads Il, and two secondary windingsinductively coupled therewith as indicated at l'i and I9. The secondarywindings ll and i9 are connected in series and a variable tuning 40capacitor 2|, connected with the high potential side of the circuit andthe secondary winding Il at 23, may be connected through a lead 25selectively with the secondary winding Il or both windings in seriesthrough a five point selector 45 switch 21 and leads 29 and 3|, thelatter being connected at a point between the series connected secondarywindings. The tap switch points are designated with the same referenceletters as the corresponding wave band adjust- 50 ment points indicatedon the receiving system in connection with the selector means l, and itwill be seen that, when the selector switch 2l is adjusted in connectionwith the points X and A, the two secondary windings are in series withthe tuning capacitor 2|. vConnected in shunt therewith, a resistor 33 oflow resistance value is inserted in circuit to be included in serieswith the winding i9.

When the switch is adjusted for the points B, C and D, the condenser isconnected directly across the winding l1 which is the main secondarywinding.

In .a radio receiver, as shown herein, the frequency response of thesystem is adjusted in the higher frequency bands as the adjusting meansis moved from the X band toward the D band. For the purpose of moreclearly understanding the operation of the system, the operating bandsfor a receiving system, such as that shown, is as follows:

Band X=140410 kilocycles Band A=5401800 kilocycles Band B=18005600kilocycles Band :5600-18000 kilocycles Band D=l800060000 kilocyclesbands B, C and D, they have an improved selectivity characteristic.

The tube I3 is thus the first intermediate frequency amplifier tube andis supplied with grid biasing potential on the control grid indicated at35 through a filter resistor 31, which may be connected with anysuitable source of biasing potential (not shown). For this purpose, theresistor 31 is connected with the lead 25 so that the connection is madein any case to the low potential side of the tuned circuit.

Sensitivity control for the radio receiving system is provided inconnection with any suitable circuit and, in the present example, isconnected with the first intermediate frequency amplifier tube as avariable bias control resistor 39 in series with the fixed self-biaspotential resistor 4| in the cathode circuit indicated at 43. Thisrepresents any suitable separate manually controllable sensitivitycontrol means in connection with the receiving system, preferably inconnection with the high frequency amplifying portion thereof.

The first intermediate frequency amplifier tube I3 is coupled through asuitable untuned interstagetransformer 45 with a second intermediatefrequency amplifier tube indicated at 41,. The

output coupling means forthe tube d1 comprises a transformer 49 andtuned secondary circuit, comprising two windings 5| and 53,corresponding to 60 the windings l1 and I9 respectively, for thepreceding stage, and a tuning condenser 55 controlled in a similarmanner by a selector switch 51 having a corresponding number of selectorpoints similarly designated. The selector point, corresponding to bandX, alone is connected through a lead 59 and a resistor 6I with thesecondary windings 53 and 5| in series. While all of the otheroonnection points for the broadcast and higher frequency bands, thesecondary alone is connected 7 in shunt with the tuning condenser. Withthis arrangement, the tuned circuit is broader only on the X band and issharper on all of the other bands. Whereas, in the preceding stage, thetun- `75 ing is broader onboth the X and A bands and is C and D.

The switches 51 vand 21 are connected for unicontrol operation with thewave band switch 1, as indicated by the dotted line connection '53, anda suitable control knob for simultaneous operation of all switches isindicated at 65. This may be considered as the wave band, selectivity,and tone control knob and in operation may be associated with thesensitivity control knob or operating device for the sensitivity controldevice 39, the said control knob being indicated at 51.

With the sensitivity control means shown, the transition to provideincreased selectivity in the higher frequency bands is madeprogressively from the signal input end of the receiver toward thedetector, which is indicated at 59, and comprises diode and triodeamplifier elements having a common cathode 1|. The diode element isprovided by a pair of diode anodes 13 connected with the tuned circuitby a suitable tap 15 on the inductance 5l, the cathode 1I beingconnected through a cathode lead 'l5 and a diode circuit impedance 11vwith the switch 51, and thence to the low potential side of the tunedcircuit either in connection with the auxiliary secondary 53 through thelead 59, or through the main secondary winding 5| by way of contacts Ato D inclusive, and a lead 19 connected at a point between the seriesconnected windings. The diode rectifier provides the second detector forthe receiver` shown, and direct current biasing potential and the audiofrequency component of the rectified signal is taken from the diodecircuit impedance or resistor 11 through a lead 8|, forming theconnection between the condenser and the switch 51 and a grid lead 83connected with a control grid 85 associated with the cathode 1|. v Ananode 81 provides, with the grid 85 and the cathode 1|, a triodeamplifier for audio frequency signals' which are transmitted throughsuitable filter elements 89 and 9| and through a suitable couplingcondenser 93 to manual tone and volume control means indicated by therectangular enclosure 95.

The anode current is supplied to the device 69 through a filterimpedance 91 and a coupling choke coil 99, this type of coupling systembeing common and well known. The tone and volume control means 95 isindependent of the wave band selector and selectivity adjusting meansand is provided with separately adjustable volume and tone control meansfor manual operation, such as control knobs |0| and |03, respectively.

The controlled audio frequency signal output from the means 95 isconveyed to a suitable multistage audio frequency amplifier through anoutput lead |05, the return connection for which is taken through a lead|01 being, a common ground return circuit for the' receiving systemcontinuing through a lead |09 and a lead Ill to the volume controlmeans.

The leads |05 and |01, therefore, constitute output leads for the systemto which the audio frequency amplifier is connected and, in the presentexample, such amplifier comprises an input transformer H3 having the lowpotential end ||5 of a primary winding H1 connected with the lead |01and ground, while the high potential end ||9 of the primary winding isconnected through a tapped inductance |2|` with the contacts A, B, C andD of a selector switch |23. The contacts B, C and D correspond to thesimilarly designated contacts of the selectivitycontrol switches andband change means and are connected with the output end terminal |25 ofthe series choke 'fio coil or inductance l2 while the contact A isconnected to a tap |21 thereon intermediateits ends.

' A contact X for said switch is connected through a lead |29 with a tap|34 on the secondary |35 of the transformer which is in turn connectedwith a pair of electric discharge amplifier devices or tubes l 33 inbalanced relation, whereby the control grid |31 of one of the push-pullamplifier tubes is connected with the lead |3| and one end terminal ofthe transformer secondary |35, while the control grid |39 of the othertube is connected to the opposite high potential side of the inputcircuit or lead Idl in turn, connected with the opposite terminal |93 ofthe transformer secondary |35. A center tap M5 is connected through aself-bias resistor |111 with the cathodes M9 of the tube |33 and is alsoconnected through a lead |5| with the ground lead |91.

The inductance i2l, which vin some steps is connected in series with theprimary winding and serves to resonate with the distributed secondarycapacitanceoi the transformer together with the lumped capacitanceconnected across the secondary by the switch, thereby producing alow-pass filter where the audio cut-olf is preceded by a response peak,caused by the lack of loading in the secondary. This peak may be used tocompensate forattenuation of the higher audio frequencies by the highfrequency amplifier.

The height of the peaks is regulated by the resistances connected inparallel with the condenser loads as in the steps C and D, for example.

The balanced or push-pull first stage amplier is coupled to a pair ofoutput amplifier electric discharge devices |5| through a push-pull o-rbalanced interstage transformer |53, providing a balanced input circuitfor the tubes |5| having input leads |55 and |51 connected with thecontrol grids |59 and |9| respectively, while the center tap |63 for thesecondary |65 is connected with a suitable source of biasing potentialindicated bythe lead |61.

The output tubes |5| are coupled in balanced relation through a suitablepush-pull or balanced output transformer |59 with an audio frequencyoutput circuit` l1! which may be `connected to any suitable outputdevice such as a loud speaker |13.

For the purpose of so controlling the signal output, the audio frequencyamplifier is provided with tone compensating means preferably in aplurality of stages, such as the rst and second stages shown, and suchcompensating means may, with greatest simplicity and at low cost, beprovided by loading the secondaries of each of the input transformersfor the succeeding stages, although other suitable tone control meansmay beused to provide a plurality of differing frequency responsecharacteristics in accordance with changes in selectivity.

In the present example, in the irst stage, a condenser resistanceloading means is provided across the input circuit in connection withthe input leads |3| and lili, under control of a tap switch having tappoints designated the same as and corresponding to those for thepreceding switches. This switch is connected through a lead |11 withoneside lill of the input circuit while the tap points are connectedsuccessively through loading means such as condensers |19, |8|, |83 and|85 through the tap points A, B, C and D, respectively, connected inparallel on the opposite side through a lead |31, in turn connectedthrough the lead |29 with the opposite side of the input circuit |3|.The condensers |83 and |85 for the points C andi) are each provided witha parallel 3. connected resistor |89 and |9|, respectively.

'I'he second or output stage input circuit is similarly loaded undercontrol of a switch |93 having a connection |95 with one side |51 of theinput circuit and having contacts X, A, B, C and D similar to the firstnamed switch through the contacts A, B, C and D of which it is connectedthrough loading condensers |91 having a common connection lead |99 withthe opposite side |55 of the input circuit. It will be noted that thecontact X, corresponding to the X wave band of each switch |15 and |93are open circuited, while the contact X of the switch |23 is connectedthrough the lead |29 with one side of the input circuit of the firststage amplier.

With this arrangement, the output circuit of the detector |05 isconnected directly through one half of the secondary winding |35 in theinput circuit of the rst stage amplifier, the return to the detectorbeing through the lead |5| and the common lead |91. The secondary of thefirst audio frequency input transformer thus becomes an auto-transformerfor more closely coupling the detector or audio frequency input circuitwith the initial audio frequency amplifier' stage.

The switches |23, |15 and |93 are interconnected as indicated by thedotted line for simultaneous uni-control operation successively throughthe five positions of adjustment of the switches, the switches being inrcorresponding positions throughout and as shown being in contact eachwith the terminal X, as is also each selectivity control switch v21 and51 and the Wave band adjustment means 1.

The audio frequency compensation control switches are furthermechanically connected with the control means 1 and theswitches 21 and51, as indicated by the dotted connection 203 whereby audio frequencycompensation and selectivity changes are made simultaneously by commoncontrol means 65. The connection is such that the wave band changes maybe made independently of the tone and selectivity changes as representedby the coupling 202 which may be released and under this condition theselectivity and tone control is effected by an auxiliary coritrol knob204. In certain receiving systems the coupling 202 may be omitted.

It will be noted that the first tone control switch |23 provides directcoupling with the secondary of the audio frequency input transformer ||3through a selected tap |34. This results in a wider response at the highend of the audio frequency` range than would be possible with the sametransformer used conventionally.

The succeeding tone control changes are arranged to includelthe seriesinductance |2| in the primary circuit either in part or wholly toresonate as hereinbefore described. l

The tone control may be arranged other than as shown in each stage toprovide any desired characteristic in predetermined relation to theselectivity.

For example in a facsimile receiver it may be desired to decrease theselectivity and increase the width of the audio response in the high endof thel audio frequency band, on the radio wave band, when the facsimilesignals are received.

The resulting response characteristics provided by the control systemshown, are indicated in Fig. 2 by five curves, each letter correspondingto the tap switch point for which it represents the outputcharacteristic of the audio frequency amplifier. 'Ihe curves areplotted, as indicated,

between frequencies in cycles per second and the audio signal responseor amplitude resulting from constant input. l

From the curves, it will be seen that with the type coupling directlywith the secondary of the input transformer and without loading, theamplifier is designed to have a substantially flat and extendedfrequency response in the upper end of the audio frequency range. Inthis position of the switch corresponding to position X, it will be seenthat the selectivityuof the high frequency' amplifier is made broader bythe inclusion in circuit of two secondary windings providing additionalcoupling means and by the use of series resistance in the intermediatefrequency amplifier.

For the position A, the second high or intermediate fr-equency circuitis caused to be more selective and the input circuit of the audiofrequency amplier is, accordingly, tuned by the inclusion of a portionof the inductance in the primary winding and` secondary loading ortuning means in each of the audio frequency amplifier stages.

The resulting increased amplitude in the region of 5,000 cycles, asshown by the curve A, serves to compensate for the reduction in the highfrequency response of the receiver, normally resulting from increasingthe selectivity whereby the response characteristic remainssubstantially fiat at the output circuit. Likewise, for the band B, Withincreased selectivity resulting from operation of the switch 21, theprimary Winding receives signals through alarger inductance comprisingthe entire choke coil or inductance I2I, While the secondaries in eachstage are more heavily loaded by condensers or other suitableA meansconnected with the point B of the switches |15 and H93.

It has been found, however, for the higher frequency receiving bands, itis desirable to reduce the high frequency response, and this isaccomplished by further loading both audio frequency stages by bothcondenser and resistance loads in the first stage through'` the contactsC and D, and by additional condenser loads in the second stage throughcorresponding contacts C and D.` The curves C and D in Fig. 2 indicatethe resulting response characteristic obtainable by the means shown.

The system shown has the further advantage that a stepped tone controlsystem both in the high frequency and low frequency circuits is providedto operate simultaneously and in predetermined mutual relation to thewave band being received to provide uniform'frequency response up to thehigh frequency end of the audio frequency range to the limit which hasbeen found practical in use without receiving undesirable interference.Y

For the reception of signals inone frequency band, it may be desirableto extend the high frequency range as indicated in Fig. 2 by the curve Xand to extend the high frequency response as far as possible in each ofthe other higher frequency ranges of signal reception, but with theadditional characteristic that each of the frequency response ranges aresharply cut-off at the predetermined limit ofthe range to be obtainedfor that wave band.

Accordingly, the wave bands or frequency response bands are adjusted bysuitable control means and the resulting change in selectivity effectedby the means provided is not only suitably compensated to provide auniform audio frequency response from the audio frequency amplier, butthe adjustment of the tone characteristic of the audio frequencyamplifier is further changed in mutual relationship thereto to providethe stepped sharpcut-off points with increased frequency response.

It should be noted that in each step the frequency characteristic may becontrolled independently of the frequency characteristic in the othersteps since separate means are provided in connection with each of theswitches, thereby providing the possibility for compensating forvariations in fidelity in the signals'received at themanual tone andvolume control means and derived therefrom to the output circuit |05 ofFig. 1.

Sincea different degree of compensation for tone or fidelity and adifferent degree of selectivity is desirable in predetermined mutualrelationship for each frequency band to be covered by the multi-rangeradio receiver, each of the control means for the selectivity and toneshould have a corresponding number of positions to be provided by thewave band selector means.

In any case, however, in accordance with the invention, the audiofrequency response range of the receiver is increased by switching theinput connection to the audio frequency amplifier from the secondary oraudio transformer connection to the primary or regular transformerconnection including series inductance for raising the responsecharacteristic at the high frequency range with sharpt cut-0H.

` Furthermore, there is thus available-in a radio receiver, arranged inaccordance with the invention, a plurality of output frequencycharacteristics, each being shaped to compensate for the selectivity ina predetermined desired relationship, and an improved and effectivecontrol of the frequency characteristic is obtained by the comblnationof controls in a plurality of stages andincluding the input circuit tothe amplifier in conjunction with the primary winding for the higherfrequency wave bands.

It will be noted that the sensitivity control means 39 is provided withindependent manual operating means such as a control knob 61.

Under certain conditions or for the reception of certain types ofsignals the sensitivity may best be changed in predetermined mutualrelationship with the selectivity in the same manner as the wave bandchange or the tone change. Hence, any suitable connection maybe made tooperate the sensitivity control means, as vby a mechanical connectionindicated bythe dotted connection line 206, having a releasable coupling208, whereby independent operation is possible. In the present examplethe connection is open for operation of the knobl 61 manuallyv andindependently.

Referring to Fig. 3, curves X1, A1, B1, C1 and D1 correspond to thecurves similarlylettered in Fig. 2 and indicate the over-all responsecharacrteristic of the amplifier of Fig. 1, in conjunction with theselectivity control means.

The dotted curves X2, A2, and the dotted curve B2 C2 D2 indicate theresponse obtainable without the compensation and the sharp cut-offfilter included in the control system of Fig. 1 for the selectivityadjustments X, A and B-C--D of the switches `21 and 51 alone. It will beseen that higher frequency noises andk undesired signals would beamplied ordinarily beyond the desired range of cut-off for each step inthe adjustment of the toney control feature and the response would notbe extended to the limit in each step as indicated by the solid linecurves. With the control arrangementshown, therefore, the result inoutput is adjustable in steps which extend the audio frequency range orreduce it as desired to predetermined limits, as the selectivity isadjusted and may also include simultaneous wave band change. Theselectivity and tone control means are connected for uni-controloperation, and the changes may be effected in desired predeterminedmutual relationship also with wave band change to produce the result inoutput as indicated by Fig. 3.

I claim as my invention:

1. In a radio receiving system adjustable for response to signals in aplurality of frequency ranges, the combination with means for providingsaid adjustment, means for tuning said system through each of saidfrequency ranges, means connected with said iirst named means forunicontrol operation therewith simultaneously to adjust the` selectivityof said system, an audio frequency amplifier, and means for adjustingthe frequency response characteristic of said audio frequency amplifierin predetermined relationship to changes in frequency range of'operation of said system, said last named means being connected withsaid first named means for conjoint uni-control operation therewith,whereby a differing degree of selectivity and a differing audiofrequency response characteristic is provided in accordance with and foreach 'differing frequency range of operation of said system.

2. In a multi-range radio receiving system, wave band selector means,high frequency amplifier means, low frequency amplifier means, and meansconnected with the wave band selector means for uni-control operationtherewith simultaneously to adjust the selectivity of the high frequencyamplifier means and the frequency response characteristic of the lowfrequency amplifier means in predetermined mutual relationship.

3. In .a multi-range radio receiving system, wave band Vselector means,high frequency amplifier means, audio frequency amplifier means, andmeans connected with the wave band selector means for uni-controloperation therewith simultaneously to adjust the selectivity of the highfrequency amplifier means and the frequency response characteristic ofthe audio frequency amplifier means in predetermined mutualrelationship, said audio frequency amplifier means comprising aplurality of electric discharge amplifier stages, a transformer having aprimary winding and a secondary winding providing an input couplingmeans for said audio frequency amplifier, and said frequency responsecontrol means comprising a selector switch for connect` ing the audiofrequency input signals directly to the secondary of said transformer toprovide an auto-transformer and alternatively to the primary winding,and a series inductance for said primary winding included in circuittherewith for said first named control means.

4. In a multi-range radio receiving system, the combination with meansfor changing the tuning range of said system, a high frequency amplifierincluding a plurality of electric discharge amplifier devices andinterstage coupling means therefor providing a series of tunablecircuits, of an audio frequency amplifier including a plurality ofstages, for receiving rectified signals through said first namedamplifier, and means for varying the selectivity of said tunablecircuits and the response characteristic of a plurality of said audiofrequency amplifier stages in predetermined mutual relationship withchange in tuning range of the system.

5. In a multi-range radio receiving system having wave band selectormeans, the combination with a high frequency amplifier including aplurality of electric discharge amplifier devices and interstagecoupling means therefor providing a series of tunable circuits, and anaudio frequency amplifier for receiving rectified signals through saidfirst named amplifier, of means for varying the selectivity of saidtunable circuits and the response characteristic of a plurality of saidaudio frequency amplifier stages in predetermined mutual relationship,said wave band selector means comprising a movable element having aplurality of selected positions of adjustment, and said selectivity andaudio frequency response control means comprising selector switchelements having a number of positions of adjustment corresponding to thewave band selector means and connected therewith for uni-controloperation, and means in circuit with said switch elements providing aplurality of differing selectivity and audio frequency tone controlcharacteristics for said system, whereby a uniform predeterminedover-all fidelity characteristic is obtained.

6. In a multi-range radio receiving system, I

having wave band selector means, the combination with a high frequencyamplifier including a plurality of electric discharge amplifier devicesand interstage coupling means therefor providing a series of tunablecircuits, and an audio frequency amplifier for receiving rectifiedsignals through said rst named amplifier, of means for varying theselectivity of said tunable circuits and the response characteristic ofa plurality of said audio frequency amplifier stages in predeterminedmutual relationship, said wave band selector means comprising a movableelement having a plurality of selected positions of adjustment, 'andsaid selectivity and audio frequency response control means comprisingselector switch elements having a number of positions of adjustmentcorresponding to the wave band selector means and connected therewithfor uni-control operation, whereby a uniform predetermined over-allfidelity characteristic is obtained.

7. A radio receiving system in accordance with claim 6, furthercharacterized by the fact that the audio frequency response controlsystem includes means in the audio frequency amplifier providing aplurality of sharp high frequency cutoff points corresponding to theseveral positions of wave band selector means.

8. In a radio receiving system having a high frequency signal amplifier,a detector and a low frequency rectified signal amplifier, thecombination with the high frequency signal amplifier of selectivitycontrol means and wave band selector means, means for changing theresponse characteristic of the low frequency amplifier simultaneouslywith the selectivity and wave band Changes under uni-control, whereby astepped tone control system is provided, and means for providing sharpcut-off points in the low frequency response characteristic at thehigher frequency end thereof with changes in adjustment of said waveband selector means.

9. In a radio receiving system, means for adjusting the frequencyresponse of said system in a plurality of differing bands, anintermediate frequency amplifier having selectivity control meanscomprising a tunable signal circuit, a switch in said circuit forvarying the selectivity and having positions corresponding to thepositionsv of adjustment of the wave band selector means, a seconddetector connected between said intermediate frequency amplifier and aplurality of electric discharge amplifier stages, providing an audiofrequency amplifier, said amplifier having an input transformer providedwith a primary winding and a secondary winding, an inductance in circuitwith said primary winding for tuning said winding, switch means forconnecting said output circuit selectively with a tap on the secondarywinding of said transformer and to said primary winding including saidinductance, selective switching means and condenser load means connectedtherewith for yshunt connection across the input circuits of at leasttwo of the stages of said audio frequency amplifier, said switcheshaving positions of adjustment corresponding to the positions ofadjustment of said wave band selector means and being connectedtherewith and with said selectivity control switch for simultaneousuni-control operation.

10. In a radio receiving system for wave band selector means, a highfrequency amplifier and a low frequency amplifier, each comprising aplurality of cascade connected stages, of selector means, forprogressively increasing the selectivity of the high frequency stageswith increase in the frequency ,of the selected wave bands, selectormeans for progressivelyloading the signal transmission circuits of theaudio frequency amplifier simultaneously with increase in frequency ofthe selected wave band, selector means for changing the audio inputcircuit from auto-transformer to transformer coupling with increase infrequency range of the selected wave band, means interconnecting saidselector means for uni-control operation, whereby the wave band changehigh frequency and audio frequency adjustments are effected thereby inpredetermined mutual relationship.

11. 'Ihe combination with a multi-range radio receiving system havingwave band selector means whereby the receiver is responsive to radiosignals in a plurality of differing wave bands, means connected with andactuated by said selector means for adjusting the audio frequencyresponse characteristic of the system, and uni-control means foradjusting the selectivity characteristic of the system in predeterminedmutual relation with the audio frequency response vcharacteristic.

12. The combination with a multi-range radio receiving system havingwave band selector means whereby the receiver is responsive to radiosignals in a plurality of differing wave bands, means for adjusting theaudio frequency response characteristic of the system, and uni-controlmeans for adjusting the selectivity characteristic of the system inpredetermined mutual relation with the audio frequency responsecharacteristic, said uni-control' means being connected with the waveband selector means whereby a predetermined over-all fidelity responsecharacteristic is obtained for each differing wave band.

1x3. In a radio receiving system, the combination with wave bandChanging of .Signal amplifier means, means for modifying the frequencyresponse characteristic of one signal amplifier thereby to modify theaudio frequency output characteristic of the system, means for modifyingthe frequency response characteristic of another of said amplifiersthereby to modify the audio frequency response characteristic fof thesystem in a differing degree, and means providing uni-control operationof said wave band changing means and modifying means, whereby theresponse characteristics are varied in predetermined mutual relation intwo differing amplij fier circuits with wave band change.

14. In a radio receiving system, the combina-A tion with wave bandchanging means, of a high frequency amplifier, a signal detectorfollowing said high frequency amplifier and an audio frequency amplifierfollowing said detector in the signal channel of said receiver,uni-control means for simultaneously adjusting the first named means,the selectivity characteristic of the high frequency amplifier and theaudio frequency response characteristic of the audio frequencyamplifier, sensitivity control means for said system, and means forconnecting said last named control means with said first named andsecond named means for uni-control operation therewith, and means forindependently varying the volume and tone characteristic of said system.

15. A radio receiving system in accordance with claim 14 characterizedby the fact that it is provided'with wave band changing means whereby itis responsive to signals in a plurality of differing wave bands, andfurther characterized by the fact that adjustment of the wave band meansis arranged to operate said uni-control means in predetermined relationto the wave band adjustment. 7

16. In a radio receiving system having a high frequency amplifier and anaudio frequency amplifier including a plurality of stages, thecombination with wave band selector means, of means for adjusting theselectivity of the system in two differing high frequency amplifierstages, means for adjusting the audio frequency response characteristicin at least two audio frequency amplifier stages, said wav'e bandselector and selectivity and audio frequency response adjusting meansbeing inter-connected and jointly controllable, and the selectivitybeing adjustable in one amplifler stage priorto adjustment in anotheramplifier stage.

17. A radio receiving system in accordance with claim 16, furthercharacterized by the fact that changes in selectivity are accompanied bypredetermined change in audio frequency characteristic, and the couplingin at least one audio frequency through an audio frequency transformerwhen the selectivity is lowest and indirectly through a couplingtransformer having a tuning inductance in series with the primarythereof when the selectivity is increased to a predetermined point.

' POUL F. G. HOLST.

